The present invention relates to gain control for receivers of mobile stations of a cellular telephone network, and more particularly to adjusting the automatic gain control (AGC) setting of a wideband code division multiple access (WCDMA) mobile station during an idle period of the serving base station in a cellular telephone network supporting the so-called Idle Period Downlink (IPDL) terminal positioning feature.
A WCDMA base station can stop transmitting in downlink (a communication from a base station to mobile stations) for a certain period of time; a period in which a base station is not transmitting is called an idle period. Associated with these idle periods is so-called idle period downlink (IPDL) functionality, which is utilized to facilitate mobile station positioning in WCDMA and is specified in more detail in 3GPP specification, TSG-RAN, TS 25.214, section 8. Idle periods are relatively short in duration and occur at regular intervals. During a succession of idle periods, a mobile station can measure signals transmitted by other, nearby base stations (not the serving base station), and based on such measurements, calculate its position. Each occurrence of an idle period of a base station is signaled to the mobile stations being served by the base station so that the mobile stations can prepare to carry out the position measurements.
Adjusting the automatic gain control (AGC) of a mobile station-during the first idle period in a succession of idle periods can be problematic. If the mobile station is close to the serving base station when the serving base station goes idle for the first time in a series of idle periods in which a position measurement is to be performed, the receiver will have a gain set to such a low value that it will detect hardly any signals from neighboring base stations. In order to receive and measure signals from the neighboring base stations during such an idle period, the AGC must be made to quickly and reliably adjust to an appropriate setting. The prior art teaches having the AGC loop (control procedure) carry out a stepwise random search of the received power, assuming no knowledge of the proper received power (except that the received power has decreased). Such a procedure can be time-consuming.
What is needed is a way to make an initial (during the first idle period of one positioning measurement session covering several idle periods) proper, rough estimate for an appropriate AGC setting. Such an estimate can then be fine-tuned later. The settling of the AGC value on an appropriate setting for other than the first idle period for a positioning measurement is straightforward, since an initial value for the AGC for each subsequent idle period is obtained from the AGC value of the previous idle period.
Accordingly, the present invention provides a system, apparatus and corresponding method for determining a setting for gain control of a mobile station in a cellular telephone network, the cellular telephone network including a plurality of base stations each having an associated cell, the base stations including the serving base station having the cell in which the, mobile station is temporarily located and also including base stations neighboring the serving base station and base stations on the active set of the mobile station, the method for use in providing a setting of the gain control for a first idle period in a succession of idle periods of the serving base station, the method including the steps of: receiving a signal from the serving base station indicating the beginning of a first idle period of the serving base station; determining whether at the location of the mobile phone the load attributable to any one of the neighboring base stations or the active set base stations differs substantially from the load attributable to at least one other of the neighboring base stations or the active set base stations, the determining being based only on information already available to the mobile station; and determining the gain control setting based on a calculation of the relative power decrease made according to a prescription that depends on whether and by how much the load attributable to any one of the neighboring base stations or the active set base stations differs from the load attributable to at least one other of the neighboring base stations or the active set base stations.
In a further aspect of the invention, if the loads attributable to each of the neighboring and active set base stations are all substantially the same, the relative power decrease is calculated using available information in a load-independent way, and, in addition, the available information includes the average energy per chip received from each neighboring and active set base station common pilot channel and the total received power spectral density including signal and interference.
In another further aspect of the invention, if the loads attributable to each of the neighboring and active set base stations are all substantially the same, the relative power decrease is calculated using,       D    =                                        G            IP                    ⁢                      s            1                          +                              ∑                          k              =              2                        n                    ⁢                      xe2x80x83                    ⁢                      E                          c              ,              k                                                            ∑                      k            =            1                    n                ⁢                  xe2x80x83                ⁢                  E                      c            ,            k                                ,
where Ec,k corresponds to the average energy per chip received from the kth neighboring or active set base station common pilot channel, where I0 is the total received power spectral density including signal and interference, and where GIP is an attenuation factor for the serving base station transmission during the idle period.
In yet another further aspect of the invention, if the loads attributable to each of the neighboring and active set base stations are not all substantially the same, the relative power decrease is calculated using available information but taking into account the variation in the loads attributable to the neighboring and active set base stations, and the available information includes the average energy per chip received from each neighboring and active set base station common pilot channel and the total received power spectral density including signal and interference.
In still yet another further aspect of the invention, if the loads attributable to each of the neighboring and active set base stations are not all substantially the same, the relative power decrease is calculated using,       D    =                                        G            IP                    ⁢                      w            1                    ⁢                      s            1                          +                              ∑                          k              =              2                        n                    ⁢                      xe2x80x83                    ⁢                                    w              k                        ⁢                          s              k                                                            ∑                      k            =            1                    n                ⁢                  xe2x80x83                ⁢                              w            k                    ⁢                      s            k                                ,
where a value of 1 for the index k indicates the serving base station, and where the wk are weights proportional to the loads attributable to the neighboring and active set base stations. In some applications implementing this aspect of the invention, the weights are given by             w      k        =          1              F        k              ,
where Fk is the ratio of the common pilot channel energy to the total transmit energy for the kth neighboring or active set base station.
From another perspective, the invention is a method for determining a setting for gain control of a mobile station in a cellular telephone network, the cellular telephone network including a plurality of base stations each having an associated cell, the base stations including the serving base station having the cell in which the mobile station is temporarily located and also including neighboring base stations, the method for use in providing a setting of the gain control for a first idle period in a succession of idle periods of the serving base station, the method including the steps of: detecting the beginning of a first idle period of the serving base station based on a signal provided by the serving base station; and determining the gain control setting based on a calculation of the relative power decrease calculated according to a prescription that uses only information already available to the mobile station.
From yet another perspective, the invention is a system for determining a setting for gain control of a mobile station in a cellular telephone network, the cellular telephone network including a plurality of base stations each having an associated cell, the base stations including the serving base station having the cell in which the mobile station is temporarily located and also including base stations neighboring the serving base station and base stations on the active set of the mobile station, the method for use in providing a setting of the gain control for a first idle period in a succession of idle periods of the serving base station, the system including the mobile station and a wireless network computational facility in wireless communication with the mobile station. The mobile station includes: means for receiving a signal from the serving base station indicating the beginning of a first idle period of the serving base station; means for determining whether at the location of the mobile phone the load attributable to any one of the neighboring base stations or the active set base stations differs substantially from the load attributable to at least one other of the neighboring base stations or the active set base stations, the determination being based only on information already available to the mobile station; and means for determining the gain control setting based on a calculation of the relative power decrease made according to a prescription that depends on whether and by how much the load attributable to any one of the neighboring base stations or the active set base stations differs from the load attributable to at least one other of the neighboring base stations or the active set base stations. The wireless network computational facility and the mobile station work together in.providing gain control in that the wireless network computational facility assists in the determinations or calculations required to determine the relative power decrease.
Thus, using the invention, the automatic gain control (AGC) settling time of a mobile station of a cellular network can be significantly shortened, making the mobile station positioning measurements that the idle period downlink (IPDL) is facilitating more effective. The invention makes an initial adjustment of the AGC of a mobile station for an idle period based on measurement information available from the serving cell for the mobile station and also based on measurement information from neighboring cells.
The main advantage of the proposed method is that the proper level/setting for the AGC can be found significantly faster than with the prior art method, so that either the total measurement time/settling time can be shorter, or the measurements can be of higher quality for the same integration time. Another advantage is that all the measurement information required for AGC is already available at a mobile station because the information needed for determining an AGC setting according to the invention is also used for other purposes.